assess what we know about the attack and explain what investigators are looking for now, we turn to juan zuarte, who was deputy national security adviser for terrorism under president george w. bush, and is now the center for strategic and international studies. and don borelli, a 25-year f.b.i. adviser who is now chief operating officer of the soufan group, which consults on security matters. juan zuarte, the president said today the investigation is in iten fancy but we know there was a pressure cooker involved, there may have been b.b.s involved, shrapnel and that maybe a circuit board was found that was used as a timer. what does this tell us about the source of this explosion? >> well, gwen, this is part of the forensic work that happens now and what authorities are looking for are signatures in the devices themselves that can give them some clues as to who may have been behind the attacks. what this tells us, at least to date, what we know is this was designed to have maximum effect. even though the explosive charge itself wasn't massive. it was designed with the ball bearings and